UK law on shipping airguns?

[R3XXY]

I'm trying to find out whether it is legal in the UK for a private individual to ship a sub-12ft lb airgun to another private individual and have had various conflicting advice. One gun shop told me that they have to go through a RFD even between private individuals, another gun shop told me that they send and receive airguns from and to customers for servicing - via Parcel Force - every day with no issues. Also, Parcel Force's own rules state that low-power airguns and lead pellets are excepted from their prohibited items.

I have looked on the UK .gov website and can't find anything regarding shipping on there, and phoned my local police HQ and they didn't know either.

Can anyone link me to a reliable source of information? I'm so confused! Help!

Thanks in advance.